Understanding the processes which regulate tissue-specific gene expression is an important issue in development biology. Currently, very little is known regarding tissue-specific gene regulation during the later stages of tooth development, especially those associated with root formation. Recent studies have identified nuclear factor I-C (NFI-C) as a critical transcription factor for normal root formation in mice and humans. NFI-C is one of four genes belonging to the NFI gene family. These genes (NFI-A, NFI-B, NFI-C and NFI-X) all exist as multiple protein products and function as cellular transcription factors and adenovirus DNA replication factors. The role of NFI-C in root formation first became evident when Nfi-c knockout mice presented with no molar root formation and severe incisor defects. In humans a similar phenotype of incomplete or absent root formation is observed in patients with the human disease Radicular Dentin Dysplasia (ROD;MIM125400) also known as Rootless Teeth or Dentin Dysplasia Type I. The inheritance pattern of this disease is described as autosomal dominant affecting both deciduous and permanent dentitions. Our laboratory has recently identified a consanguineous family with a novel autosomal recessive (AR) form of ROD. The proband presented with premature exfoliation of his teeth. Dental x-rays revealed no development of any root structures associated with the deciduous or permanent teeth. DNA sequencing analysis of the AR ROD family revealed a mutation in the 3'untranslated region (UTR) of NFI-C. This mutation, contained within an element highly conserved across all available species, results in decreased NFI-C mRNA levels. The unique root phenotype in the Nfi-c null mouse and identification of a NFI-C mutation associated with pathogenesis of AR ROD suggests that NFI-C is a critical transcription factor for inductive epithelial mesenchymal signaling leading to root formation. Our hypothesis is that the NFI-C gene expression is regulated in part by a conserved element contained within the 3'UTR region of the gene and that a mutation in this regulatory element results in decrease levels of the protein altering normal signaling cascades for root formation. The information obtained from these studies will provide a foundation for understanding the molecular mechanisms involved in normal tooth root development, as well as the root phenotype found in patients presenting with ROD. Eventually the proposed studies will facilitate the development of novel diagnostic tools and therapeutic treatments for patients with various diseases or syndrome with altered root formation.